The field of the invention is small portable antennas. An antenna or antenna assembly of the invention is used in small portable devices, e.g., wireless network portable phones.
Worldwide availability of wireless services has created a demand for wireless network phones which are operable worldwide. In different regions of the world there are different frequency allocations. A phone which is operable in each of the different regions requires either multiple antennas or a multi-band antenna which covers the frequency allocations. Multiple band antennas are a better option because wireless network portable phones benefit from compact antennas.
Performance of compact single band and multiband antennas is dependent upon repeatable manufacturing. A key component in multiple band antennas is a helical radiator. Mechanical tolerances for the manufacture of helical radiators have become more exacting as the electrical performance demands of a helical radiator have changed to complement multiband antenna designs. Maintaining proper dimensions oil a helix, e.g., the pitch, diameter, and length, is difficult using conventional spring making machines.
It is also important to have an antenna assembly which is simple to manufacture, as this reduces manufacturing costs. Thus, there is a need for an improved antenna assembly including a helical radiator.
A compact antenna assembly of the invention includes a helical radiator wound around a nonconductive core plug to provide a desired pitch or pitches in the helical radiator. A preferred compact antenna assembly of the invention includes a nonconductive hollow core plug. The core plug has a recessed pattern on an outside surface into which a helical radiator is wound. An end portion of the helical radiator extends through a hole in the core plug to contact a center radiator extending in the hollow portion. A cover covers the helical radiator. Preferably, the entire assembly is configured to snap-fit together and to a device. The cover and core plug may snap-fit together. The bottom of the core plug may define a mount and the center radiator may be exposed from the mount as a device contact. The center radiator is also preferably shaped to grab onto the helical radiator with a snap-fit.
Such an assembly produces a reliable and convenient assembly method as well. The recess pattern and hole on the core plug allow formation of the helical radiator having the exact pitch defined by the recess pattern by inserting a wire into the hole and applying pressure to the wire while rotating the core plug and wire vis a vis each other to wind the wire into the recess pattern. The cover and core plug are then attached.
Preferred snap-fit connections between the core plug and cover facilitate joining of the antenna assembly together, while a preferred snap mount formation on a bottom portion of the core plug similarly facilitates joining of a finished assembly to a device. In addition, the snap-fit connection between the core plug and cover preferably permits the cover to rotate freely. Where the preferred assembly includes a center radiator that defines a spring contact to a device, the snap-fit joining of a bottom mount portion will also produce reliable electrical contact to a device.
In another aspect of the invention, a configuration of the helical radiator has three separate sections defining three separate radiator stages. This aspect of the invention may be used with the assembly described above having the recess for forming a helical radiator, or it may be used as part of a more basic assembly having the multi-stage helical radiator wound on a core plug. A cover is attached to the core plug to cover the helical radiator. An electrical contact contacts the helical radiator and is exposed from the core or cover for contact to a device.
The helical radiator including separate lower, middle and upper sections respectively having separate lower, middle and upper pitch angles provides multiple band operation. A length of the lower section determines a resonance frequency of a high band. The middle section serves as a choke with high impedance at high bands and low impedance at low bands. The total wire length of the lower, middle and top sections determines a low band resonance frequency. This aspect of the invention permits double band, e.g., AMPS/GSM, or triple band, e.g., AMPS/GSM/PCS, operation. An increase of the bandwidth in the high band to realize quad band operation with adjacent high bands and adjacent low bands, e.g., AMPS/GSM/DCS/PCS or AMPS/GSM/DCS/WCDMA, may be realized with the center radiator discussed above. With a center radiator, the three stage helical radiator forms an antenna in which the high band resonance frequencies are determined together by the length of the lower section of the helical radiator and the length of the central radiator from the point where the helical radiator electrically contacts the central radiator. The low band frequencies are determined by the total length of the helical radiator as in the case where the center radiator is absent.